Session: 12-03-03: General: Mechanics of Solids, Structures and Fluids

Paper Number: 144893

144893 - Structural Investigation of an Additively Manufactured Stator of a Transverse Flux Machine 

The transverse flux machine (TFM) is an electric machine that efficiently utilizes the available space by splitting the paths of the magnetic flux and the electric current. Compared to a permanent magnet synchronous motor, a TFM has a higher torque density, which makes it beneficial for small scale or lightweight applications, where typically a gearbox is required.

The stator of a preceding generation of a TFM was manufactured by soft magnetic composites. Recent research focused on additively manufactured stator geometries for an increased design flexibility. The use of additively manufactured bulk iron introduces the problem of high eddy current losses. Slits incorporated into the stator geometry mitigate these losses. However, they strongly influence the structural integrity of the stator. Up until now, the structural integrity was not accounted for in the design of the stator geometry. In addition, the keyed shaft-hub connection has not been considered in the electromagnetic design of the stator, assuming that it has no large effect on the electromagnetic properties. This paper examines the structural mechanics of the stator of the current design iteration of the TFM, including alternating slits in the stator to reduce eddy current losses.

The electromagnetic simulations were conducted on a symmetric section containing a single pole pair. To investigate the keyed shaft-hub connection, a simulation of a full stator geometry is necessary, since a rotational symmetry is no longer given. However, an electromagnetic simulation of a full stator geometry is computationally expensive, so we developed a method to transfer the acting forces from a single pole pair to the whole stator geometry. In this method, the geometry is divided into different patches with a uniform force distribution. The surface-averaged forces in each patch are then transferred from the single pole pair to the full stator simulation model. This enables the use of different meshes for the electromagnetic and the structural simulation.

Results of the structural simulation showed that the stresses are in an acceptable range and that a stress concentration can be seen close to the parallel keyway. The slitted stator with a keyed shaft-hub connection experiences a strong deformation. This deformation can lead to a local separation between stator and hub and a contact between stator and rotor. Molding the stator and coil in epoxy resin reduces the deformation, but the deformation remains highly asymmetrical. Furthermore, common construction guidelines advise against a keyed shaft-hub connection with alternating torque transmission, as occurs in a TFM.

Therefore, we investigated the use of a polygonal shaft-hub connection. We based the geometry on the standard DIN 32712. Electromagnetic simulations showed, that the altered geometry has only a small negative effect on the electromagnetic behavior and therefore the efficiency of the TFM. The maximum deformation of the stator geometry is halved compared to the keyed shaft-hub connection. In addition, the deformation along the outer surface of the stator is symmetric, which is beneficial for the electric control of the TFM.

In conclusion, we showed that the current geometry of an additively manufactured stator of a TFM with integrated slits for eddy current loss reduction has not enough structural integrity. Molding the stator and coil with epoxy resin improves the integrity, but further reduction of the deformation is necessary. A polygonal shaft-hub connection shows promising results while having little effect on the electromagnetic efficiency. In future works, we want to manufacture and validate the stator with a polygonal shaft-hub connection. Furthermore, the orientation of the slits to reduce eddy current losses is depending on the magnetic flux through the stator geometry, so new slit trajectories must be created.

Presenting Author: Simon Knecht Institute of Product Engineering, Karlsruhe Institute of Technology

Presenting Author Biography: Simon Knecht studied Aerospace Engineering at the University of Stuttgart with a focus on numerical methods and computational fluid dynamics. After working in the industry for a year as a simulation engineer, he started working for his PhD thesis at the Institute of Product Engineering at Karlsruhe Institute of Technology. In his research, he focusses on numerical simulation and optimization of complex systems, such as electro-hydraulic actuators and electric motors.

Authors:

Simon Knecht Institute of Product Engineering, Karlsruhe Institute of Technology
Martin Schmid Institute of Electrical Energy Conversion, University of Stuttgart
Isabell Reisch Institute of Electrical Energy Conversion, University of Stuttgart
Nejila Parspour Institute of Electrical Energy Conversion, University of Stuttgart
Albert Albers Institute of Product Engineering, Karlsruhe Institute of Technology